Polyurethane foams have been widely used as heat insulating materials for electric refrigerators, freezers, cold storages, building material panels, etc. because of their excellent heat insulation performance, moldability and self-adhesion properties, and they have been widely used for interior trim materials, such as sheet cushions, sheet backs, headrests, armrests, instrument panels, door trims and ceiling materials of vehicles such as automobiles, bicycle saddles, air planes, sheet materials for railroad vehicles, furniture, bedding, and office supplies, such as cushioning materials of business chairs, because of their excellent cushioning properties.
Polyurethane foams are obtained by preparing a resin premix containing a polyol such as a polyoxyalkylene polyol or a polymer polyol (polymer-dispersed polyol), a catalyst for polyurethane foam production, a blowing agent, etc. and allowing this resin premix to react with a polyisocyanate. The polyoxyalkylene polyol is obtained by, for example, addition polymerization of an alkylene oxide compound onto an active hydrogen compound using a basic catalyst.
To the polyoxyalkylene polyol, a stabilizer such as an antioxidant is usually added for the purpose of preventing oxidation deterioration of the polyol or in order not to form a peroxide that inhibits reactivity of the catalyst for polyurethane foam production. Such a stabilizer is, for example, a phenol-based compound (see, for example, patent literature 1).
When a catalyst or an acid derived from the polyol is contained in a resin premix for a long period of time, various problems such that the resin premix is color-changed to yellow or brown with time, the component contained in the resin premix is crystallized and precipitated, and separation between an aqueous layer and an organic layer occurs in the resin premix are usually liable to take place. Further, when a large amount of the catalyst is contained in the resin premix, the catalyst has influence on the urethanation reaction during the production of a polyurethane foam, and as a result, there is a fear of difficult control of the reaction time or a fear of evil influence on the performance or the moldability of the foam.
The phenol-based compound is widely used as an additive added to a polyoxyalkylene polyol, but in general, it tends to be discolored under the basic conditions, particularly in a resin premix or a polyoxyalkylene polyol containing a basic catalyst used for polymerization.
On that account, in general, the polyoxyalkylene polyol containing the catalyst is not used as it is in the resin premix, and for example, it is commonly carried out to neutralize the catalyst contained in the polyoxyalkylene polyol with an acid or the like and to purify the polyoxyalkylene polyol to reduce the amount of the catalyst, the acid component, etc. to a certain level or lower, prior to use for the resin premix (patent literatures 2 to 5, etc.).
However, a removal step, a purification step, etc. are required, and the process is extremely complicated.
Therefore, development of a resin premix, which is capable of producing a urethane foam without any problem even if it contains a catalyst, an acid and a stabilizer such as an antioxidant and which is excellent in long-term storage stability, has been desired.